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IGNEOUS ROCKS Igneous – derived from the Latin word ignis, meaning Fire. IGNEOUS ROCKS Lava is molten rock found at or near Earth’s surface. Magma is molten rock found beneath Earth’s surface. Igneous Rocks form from both lava and magma. 3 Ways Magma Can Form • Pressure – The high pressure inside Earth causes Hot rocks and minerals to remain solid. When those hot rocks rise and the pressure lowers, the minerals melt. • Temperature – High temperatures melt minerals. Each mineral has a different melting point – so some minerals melt when others remain solid. • Composition – If fluids, such as water, combine with the rock, the composition of the rock changes which lowers the melting point enough for it to melt and lower temperatures. Igneous Rock • Forms when hot, liquid rock or magma, cools and solidifies • Found near volcanic activity • Liquid magma is a mixture of many minerals Intrusive & Extrusive Those igneous rocks that form from magma are referred to as INTRUSIVE. INTRUSIVE = Inside Those igneous rocks that form from lava are referred to as EXTRUSIVE. EXTRUSIVE = Outside Extrusive Intrusive Magma TEXTURE of Igneous Rocks • Determined by how fast the magma cools • Smooth grained rocks are formed by magma that cools quickly (Extrusive) • Coarse grained rocks are formed when magma cools slowly (Intrusive) IGNEOUS ROCK FORMATIONS Intrusive Extrusive • Form Below Earth’s surface and inside the Earth • Forms on the Earth’s surface • Intrusive rocks have a coarse grained texture because ? • Extrusive rocks have a smooth texture because ? COMPOSTITION of Igneous Rocks • Light colored rocks are less dense and rich in Quartz Felsic (aluminum, potassium, silicon and sodium) • Dark colored rocks are more dense and contain Plant Nutrients. (calcium, iron, magnesium) Mafic Igneous Rock QUESTION Obsidian is a dark-colored volcanic glass that forms from the very rapid cooling of molten rock material. It cools so rapidly that crystals do not form. • Is this rock Felsic or Mafic? • Is it fine-grained or coarse-grained? • Is this rock Intrusive or Extrusive? Mafic, fine grained, extrusive Andesite – Fine-grained, extrusive Felsic igneous rock Basalt is also an abundant rock on the Moon. Much of the Moon's surface is underlain by basaltic lava flows and flood basalts. These areas of the Moon are known as "lunar maria." Basalt – Fine-grained, extrusive Mafic Diorite – Coarse-grained, intrusive. Mixture of Mafic and Felsic Gabbro – Coarse-Grained, intrusive, Mafic igneous rock Pumice – Extremely Fine-Grained, Extrusive Felsic Igneous Rock Form during explosive volcanic eruptions from the cooling of the frothy magma Forms when some volcanoes erupt, a rush of gas blows out of the vent. This gas was once dissolved in the magma below. The gas often blows out small bodies of magma that solidify as they fly through the air. Scoria – Extremely fine-grained, Extrusive Mafic Igneous Rock
